#4 boot IO.SYS from drive 0x1 (B:)

[Anonymous]

chainloader --edx=0x01 (fd1)/io.sys
Will boot MS-DOS 7.x from drive=0x0

it seems that --edx option doesn't correctly set drive
number except 7th bit (hdd flag - 0x80):

chainloader --edx=0x80 (fd1)/io.sys
Will boot MS-DOS 7.x from drive=0x80

chainloader --edx=0x81 (fd1)/io.sys
Will boot MS-DOS 7.x from drive=0x80

therefore DOS can't find command.com and doesn't
process config.sys and autoexec.bat